1. Field of the Invention
The present invention relates to a connection method and a substrate. More particularly, the present invention relates to a connection method capable of reducing reflection due to impedance unmatching in a connection part and satisfactorily maintaining signal quality in a case where, for example, electronic parts are to be mounted on a substrate, and to a substrate for use therewith.
2. Description of the Related Art
Connection structures between parts and substrates are broadly divided into the following two types. One type is a completely shielded structure like a coaxial cable, and the other type is an open structure in which inductive capacity exists between signal lines like wiring on a substrate.
Although the latter open structure is inferior to a coaxial structure from the viewpoint of crosstalk and electromagnetic interference, it is a practical structure which is advantageous in terms of industrial cost incurred for design, manufacture, and inspection, and in terms of connection properties, as can be understood when compared with ordinary printed wiring substrates.
However, in the shape of lines of an open structure, when handling a high-speed signal, deterioration of a transmission signal becomes a significant problem. In particular, as shown in FIG. 1, in a connection part between an electronic part that is surface mounted on a substrate and a substrate, a transmission signal is likely to be attenuated/deteriorated due to the influence of a reflected wave caused by impedance unmatching.
By forming wiring to be a line structure like a microstrip, it is possible to adjust impedance so as to deal with a high-speed signal. However, in the case of mounting between layers/substrates/parts having different heights, it is necessary to extend a terminal portion from the part side as shown in FIG. 2, or it is necessary to form a viahole from a solder ball as shown in FIG. 3, thereby being connected to the wiring on the substrate. Therefore, in a connection part between a part and a substrate shown in FIG. 1, it is not possible to maintain a line structure through which impedance can be adjusted, and it is difficult to avoid deterioration of signal quality.
As a method of adjusting impedance in a connection part, a method disclosed in Japanese Unexamined Patent Application Publication No. 2000-216510 exists.